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United States Department of Agriculture

Agricultural Research Service

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Research Project: Genetic Improvement of Prunus and Vitis Scions and Rootstocks for Fruit Quality and Pest Resistance

Location: Crop Diseases, Pests and Genetics

2013 Annual Report


1a.Objectives (from AD-416):
The overall goal of the proposed research is the development and introduction of new high quality and disease resistant cultivars of almonds, grapes and stone fruits that will sustain American agriculture and supply high quality, nutritious fruits and nuts to US consumers and international markets. This goal was validated, and ranked as a high-priority ‘researchable objective’ by stakeholders attending the 2011 Program Visioning Conference held at the San Joaquin Valley Agricultural Sciences Center. Specifically, over the next five years we will focus on the following objectives:

Objective 1: Evaluate table and raisin grape germplasm with putative resistance to powdery mildew for superior fruit quality and field resistance to powdery mildew under commercial conditions.

Objective 2: Evaluate fruit quality of dry-on-vine (DOV) raisin selections and of “teinturier” type table and raisin selections.

Objective 3: Develop superior Prunus rootstocks with resistance to economically important soilborne pests and excellent graft compatibility, desirable scion vigor, and excellent production potential.

Objective 4: Select and evaluate new high quality scion cultivars of Prunus (almond, apricot, peach, and plum) from currently available breeding crosses.


1b.Approach (from AD-416):
Classical breeding techniques have been used to create segregating populations where the expression of quantitative traits has been concentrated and newly available characters have been transferred into adapted Prunus and Vitis germplasm. Seedlings in existing segregating populations of Prunus and Vitis will be selected and propagated for new cultivar development. Greenhouse and field screening will proceed to select Vitis seedlings with resistant to powdery mildew. Molecular markers will be used to identify those Vitis seedlings with multiple sources of powdery mildew resistance. Resistance to powdery mildew and Pierce’s Disease will be combined through hybridization of appropriate vines. Hybridizations will continue for production of both dry on the vine and red flesh color in grapes. Apricots will be selected for drying ability and for late maturity season from all remaining segregating progenies. New self-compatible almonds will be selected from segregating populations that have kernel qualities similar to Nonpareil, and four high kernel quality self-compatible almond selections will be trialed in three locations in the San Joaquin Valley. Hybridization will be repeated if necessary, to achieve population sizes necessary for identifying and selecting elite germplasm or for the development of molecular markers linked to traits of interest.


3.Progress Report:
This research represents a continuation of research from former Project No. 5302-21220-005-00D entitled "Improvement of Prunus and Vitis Scions for Fruit Quality and Pest Resistance". Evaluations continued for a second year involving nine apricot accessions on two rootstocks. Bloom timing and harvest interval data are being collected, as well as basic fruit quality and yield parameters. Remaining apricot populations are being rogued of fruiting seedlings that demonstrate obvious defects that limit usefulness as fresh market or dry products. Evaluations are continuing in a low-chill apricot variety trial at Riverside, California. The 2013 fruit season marked the first commercial crop from the plot, and all six varieties required some degree of fruit thinning to standardize crop loads.

Support from table grape and raisin commodity groups permitted hybridizations during the 2012 bloom interval, with 114 separate crosses performed among elite breeding parents. Seedlings from appropriate populations were screened for powdery mildew resistance in the greenhouse. All powdery mildew resistant seedlings have been field planted.

Over 550 seedlings and advanced grape selections were evaluated during the fruiting season. These included vines with field resistance to powdery mildew and selections with red-colored (teinturier) flesh. A total of 83 dried on the vine (DOV) raisin selections fruited and were evaluated in 2-vine plots. Of these, 35 were sufficiently dry for harvest during the first week of October. The most advanced natural DOV selection being trialed in 27-vine plots was harvested at the onset of October, averaged 4.0 tons per acre at approximately 12% moisture and graded 86% saleable raisins. Four new DOV powdery mildew resistant raisins were selected for propagation into 7-vine plots during the 2012 harvest.

Eight newly-available commercial Prunus rootstocks have been proliferated in micropropagation in sufficient quantity to provide rooted explants for in-vitro screening against oak root rot fungus. Twelve new Prunus hybrids initially established through ovule culture are now being proliferated to provide clones for future screening against soilborne pests.


Last Modified: 10/25/2014
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